Balancing ssd wear in data storage systems

ABSTRACT

A technique for use in balancing flash drive wear in data storage systems is disclosed. multiple sets of flash drives are identified where data is stored as multiple slices striped across the set of flash drives. A write rate at which data will be written to the multiple slices stored on the set of flash drives during a next time interval is predicted. A number of bytes that can be written to each set of flash drives is determined. A metric representative of a wear rate is determined for each set of flash drives. Flash drive wear rate is balanced such that the wear rate for each of the multiple is approximately equal.

TECHNICAL FIELD

The present invention relates to balancing solid state drive wear indata storage systems.

BACKGROUND OF THE INVENTION

Storage devices are employed to store data that are accessed by computersystems. Examples of basic storage devices include volatile andnon-volatile memory, floppy drives, hard disk drives, tape drives, andoptical drives. A storage device may be locally attached to aninput/output (IO) channel of a computer. For example, a hard disk drivemay be connected to a computer's disk controller. A storage device mayalso be accessible over a network. Examples of such storage devicesinclude network attached storage (NAS) and storage area network (SAN)devices. A storage device may be a single stand-alone component or becomprised of a system of storage devices such as in the case ofRedundant Array of Inexpensive Disks (RAID) groups.

A traditional RAID group is a collection of hard disk drives operatingtogether logically as a unified storage device, e.g., to provide somedata protection through redundancy. Storage devices with RAID groups aredesigned to store large quantities of data and typically include one ormore storage array processors (SPs), for handling both requests forallocation and IO requests.

Many computing devices now include non-volatile memory (NVM), such ascertain magnetic, semiconductor, and/or optical storage media, and mayinclude removable disk systems, hard drives, and other storage mediasystems allowing the device and/or a user to store data the device usesor is directed to use. The characteristics of non-volatile,vibration-free, small size, and low power consumption have made a typeof NVM known as flash memory an excellent component to be utilized invarious storage systems.

Flash storage devices are widely used as memory storage for consumersystem products such as a notebook, desktop computer, set top box,digital camera, mobile phone, PDA and GPS. The increasing demand formore storage in these products has driven the need to expand thecapacity of flash storage devices.

Advances in flash semiconductor technology continue to decrease the costper unit and increase the capacities of flash devices. Further, flashdevices can provide a significant performance advantage over magneticdisk media in many storage system applications. As cost continues todecrease, there is an industry shift underway towards the use ofsemiconductor solid state drives (also known as solid state disks orSSDs) using flash memory devices as a storage media in storage arrays.

An SSD has many features that can make it an attractive storage device.For example, SSDs have a fast access rate, high throughput, a highintegration density, and stability against an external impact. SSDs canmove large amounts of data and process a large number of IO requests.This allows users to complete data transactions much more quickly. Thus,in at least some cases, there has been an increasing trend towards theuse of SSDs as storage devices instead of, or in addition to, magneticdisks.

However, unlike an HDD employing magnetic disks, SSDs utilizing flashmemory devices have a limited number of program/erase (PE) cycles (alsoreferred to as writes or write operations) before the SSD becomesunreliable. The number of PE cycles can vary and SSDs may be categorizedbased on their number of PE cycles. For example, an SSD may beclassified as low endurance (LE), medium endurance (ME) or highendurance (HE) SSD.

SUMMARY OF THE INVENTION

A technique for use in balancing flash drive wear in data storagesystems is disclosed. multiple sets of flash drives are identified wheredata is stored as multiple slices striped across the set of flashdrives. A write rate at which data will be written to the multipleslices stored on the set of flash drives during a next time interval ispredicted. A number of bytes that can be written to each set of flashdrives is determined. A metric representative of a wear rate isdetermined for each set of flash drives. Flash drive wear rate isbalanced such that the wear rate for each of the multiple isapproximately equal.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become moreapparent from the following detailed description of exemplaryembodiments thereof taken in conjunction with the accompanying drawingsin which:

FIG. 1 is an example of a system that may utilize the techniquedescribed herein;

FIG. 2 is an example representation of physical and logical views ofentities in connection with storage in an embodiment in accordance withtechniques herein;

FIGS. 3, 4, and 5 are block diagrams illustrating aspects of implementthin or virtually provisioned logical devices in an embodiment inaccordance with techniques herein;

FIG. 6 is an example illustrating data and software components that maybe used in an embodiment in accordance with techniques herein;

FIGS. 7 and 8 are graphical representations illustrating an exampleembodiment that may utilize the techniques described herein;

FIG. 9 is an example of a system that may utilize the techniquedescribed herein; and

FIG. 10 is a flowchart of the technique performed in accordance withtechniques described herein.

DETAILED DESCRIPTION

Data storage systems may include different types of storage devices,such as solid state drives (SSDs) and hard disk drives. SSDs aretypically specified as having an expected lifetime (e.g., as measured inan amount of actual elapsed time such as a number of years or months)based on a number of guaranteed write cycles at a particular rate orfrequency at which the writes are performed. Thus, an SSD may have aspecified lifetime rating expressed in calendar or wall clock elapsedtime based on the amount of time it takes to perform the number ofguaranteed write cycles. SSDs comprising flash memory devices may alsobe referred to herein as flash drives; however the techniques describedherein may utilize SSDs that employ other memory technology such asnonvolatile Random Access Memory (NRAM), phase-change RAM (PRAM),ferroelectric RAM (FERAM), magnetoresistive RAM (MRAM),resistance-change RAM (RRAM). and the like.

An SSD may be specified as having a physical size and a logical size.The physical size (also referred to herein as “physical space”) orcapacity represents the total amount of memory available on the device.The logical size (also referred to herein as “logical space”) is theamount memory allocated to a user for storing user data. The remainingamount of space is reserved for data management processes, and may bereferred to herein as over-provisioning. For example, physical size maybe 256 GB and the logical size may be 200 GB. The remaining 56 GB may bereserved for over-provisioning.

Logical to physical size is typically chosen such that the SSD can meeta particular specification, such as a rated lifetime specification basedon an expected rate at which the writes will be performed. Theallocation of over-provisioning space to logical space may be expressedas a ratio and varies based on intended application taking into accountdesired endurance and performance characteristics (as used herein, suchratio may be referred to as “over-provisioning ratio” or “allocationratio”). For example, over-provisioning values may vary from as low as2-5% for inexpensive consumer applications to upwards of 60-70% forhigh-performance MLC flash enterprise applications.

An SSD can be queried to determine the drive's effective write rate.Wear rate may be monitored based upon a particular implementationcriteria. For instance, wear rates may be monitored hourly, daily,weekly, or monthly as desired based upon operating demand placed on thesystem. For example, querying an SSD may indicate that it's been writtento 10 K times after one month of operation. If writes continue at thesame rate, the SSD will be written to 120 K times per year. After fiveyears, a common warranty period, the SSD will be written to 600 K times.If the SSD is warranted for say 500 K writes, the SSD can be expected tofail in less than 5 years which would be within the warranty period,resulting in increased maintenance costs and a dissatisfied customer.

Advantageously, techniques described herein disclose a method toestimate the rate at which writes will occur to a particular SSD. Thewarranty period for the SSD can be determined. The technique furtherdetermines if writes at the estimated rate will result in reaching theSSD's end of warranty period before the warranty period expires. If so,data can be moved to drives having a lower write rate. The method may beperformed across substantially all a storage array's SSDs such thatsubstantially all the SSDs will wear at the same rate, therby balancingwear across all the SSDs.

For example, consider the scenario where writes are estimated at say 4 Kper month, or 48 K per year. If the SSD drive is rated for 500 K writesover its lifetime, and writes continue at this rate, the drive may lastover 10 years. In this case, the amount write activity may be increased,thereby, improving system performance by increasing the rate at whichwrites are directed to the SSD. However, if writes are estimated tooccurs at say 120 K per year, or 600 K in 5 years, the drive may wearout before the end of the 500 K write warranty period. In this case, thewrite wear rate can be reduces by relocating slices (e.g., write heavyslices) to a different SSD experience a lower write rate.

Consequently, employing techniques described herein may be used toincrease and/or decrease the wear rate for multiple SSDs to balance wearacross the multiple SSDs and potentially improve system performance. Inthis case, the technique may be used to monitor the rate at which writesare directed to an SSD and if it is determined that the rate is highenough such that the drive may be expected to fail sooner than expected,logical space can be decreased to slow the number of writes directed tothe drive and in create the relative amount of over-provisioning spaceavailable for data management and storage operations. As a result, themethod will slow the rate at which the SSD wears. If it is determinedthat the writes are so low such that the expected lifetime of the driveis significantly beyond the intended use, and performance may beimproved by increasing the number of writes directed to the SSD. Bycontinuously monitoring the rate, the amount of memory allocated forlogical space may be increased or decreased in order to tailor the wearrate so as to ensure the SSD lasts as long as intended while providingmaximum performance during its lifetime.

Advantageously, the techniques can allow a data storage system tobalance the SSD wear rate by dynamically adjusting the wear rate asworkloads change. Such changes may occur over time. For example,workloads may increase when the system is first put into production. Asapplications and data are loaded onto the system and as the system rampsup, it stores more and more data thereby approaching capacity. In thiscase, it may be desirable to reduce or slow the rate at which data iswritten to the system. Alternatively, workloads may decrease as newsystems are installed. Applications and data may be moved from one ormore existing system onto the new system thereby decreasing workloads onthe existing system. As the storage system reaches end-of-life,applications may continue to be migrated elsewhere thus reducing thewear rate and, in this case, memory allocated for capacity may beincreased to provide additional performance boost.

Referring to FIG. 1, shown is an example of an embodiment of a systemthat may be used in connection with performing one or moreimplementations of the current techniques described herein. The system10 includes a data storage system 12 connected to host systems 14 a-14 nthrough communication medium 18. In this embodiment of the computersystem 10, the n hosts 14 a-14 n may access the data storage system 12,for example, in performing input/output (IO) operations or datarequests. The communication medium 18 may be any one or more of avariety of networks or other type of communication connections as knownto those skilled in the art. The communication medium 18 may be anetwork connection, bus, and/or other type of data link, such as ahardwire, wireless, or other connections known in the art. For example,the communication medium 18 may be the Internet, an intranet, network(including a Storage Area Network (SAN)) or other wireless or otherhardwired connection(s) by which the host systems 14 a-14 n may accessand communicate with the data storage system 12, and may alsocommunicate with other components included in the system 10.

Each of the host systems 14 a-14 n and the data storage system 12included in the system 10 may be connected to the communication medium18 by any one of a variety of connections as may be provided andsupported in accordance with the type of communication medium 18. Theprocessors included in the host computer systems 14 a-14 n may be anyone of a variety of proprietary or commercially available single ormulti-processor system, such as an Intel-based processor, or other typeof commercially available processor able to support traffic inaccordance with each particular embodiment and application.

It should be noted that the particular examples of the hardware andsoftware that may be included in the data storage system 12 aredescribed herein in more detail, and may vary with each particularembodiment. Each of the host computers 14 a-14 n and data storage systemmay all be located at the same physical site, or, alternatively, mayalso be located in different physical locations. The communicationmedium that may be used to provide the different types of connectionsbetween the host computer systems and the data storage system of thesystem 10 may use a variety of different communication protocols such asSCSI, Fibre Channel, PCIe, iSCSI, NFS, and the like. Some or all of theconnections by which the hosts and data storage system may be connectedto the communication medium may pass through other communicationdevices, such as a Connectrix or other switching equipment that mayexist such as a phone line, a repeater, a multiplexer or even asatellite.

Each of the host computer systems may perform different types of dataoperations in accordance with different types of tasks. In theembodiment of FIG. 1, any one of the host computers 14 a-14 n may issuea data request to the data storage system 12 to perform a dataoperation. For example, an application executing on one of the hostcomputers 14 a-14 n may perform a read or write operation resulting inone or more data requests to the data storage system 12.

It should be noted that although element 12 is illustrated as a singledata storage system, such as a single data storage array, element 12 mayalso represent, for example, multiple data storage arrays alone, or incombination with, other data storage devices, systems, appliances,and/or components having suitable connectivity, such as in a SAN, in anembodiment using the techniques herein. It should also be noted that anembodiment may include data storage arrays or other components from oneor more vendors. In subsequent examples illustrating the techniquesherein, reference may be made to a single data storage array by avendor, such as by EMC Corporation of Hopkinton, Mass. However, thetechniques described herein are applicable for use with other datastorage arrays by other vendors and with other components than asdescribed herein for purposes of example.

The data storage system 12 may be a data storage array including aplurality of data storage devices 16 a-16 n. The data storage devices 16a-16 n may include one or more types of data storage devices such as,for example, one or more disk drives and/or one or more solid statedrives (SSDs). An SSD is a data storage device that uses solid-statememory to store persistent data. An SSD using SRAM or DRAM, rather thanflash memory, may also be referred to as a RAM drive. SSD may refer tosolid state electronics devices as distinguished from electromechanicaldevices, such as hard drives, having moving parts. Flash memory-basedSSDs (also referred to herein as “flash disk drives,” “flash storagedrives”, or “flash drives”) are one type of SSD that contains no movingmechanical parts.

The flash devices may be constructed using nonvolatile semiconductorNAND flash memory. The flash devices may include one or more SLC (singlelevel cell) devices and/or MLC (multi level cell) devices.

It should be noted that the techniques herein may be used in connectionwith flash devices comprising what may be characterized asenterprise-grade or enterprise-class SSDs (EFDs) with an expectedlifetime (e.g., as measured in an amount of actual elapsed time such asa number of years, months, and/or days) based on a number of guaranteedwrite cycles, or program cycles, and a rate or frequency at which thewrites are performed. Thus, a flash device may be expected to have ausage measured in calendar or wall clock elapsed time based on theamount of time it takes to perform the number of guaranteed writecycles. The techniques herein may also be used with other flash devices,more generally referred to as non-enterprise class flash devices, which,when performing writes at a same rate as for enterprise class drives,may have a lower expected lifetime based on a lower number of guaranteedwrite cycles.

The techniques herein may be generally used in connection with any typeof flash device, or more generally, any SSD technology. The flash devicemay be, for example, a flash device which is a NAND gate flash device,NOR gate flash device, flash device that uses SLC or MLC technology, andthe like, as known in the art. In one embodiment, the one or more flashdevices may include MLC flash memory devices although an embodiment mayutilize MLC, alone or in combination with, other types of flash memorydevices or other suitable memory and data storage technologies. Moregenerally, the techniques herein may be used in connection with otherSSD technologies although particular flash memory technologies may bedescribed herein for purposes of illustration. For example, consistentwith description elsewhere herein, an embodiment may define multiplestorage tiers including one tier of PDs based on a first type offlash-based PDs, such as based on SLC technology, and also includinganother different tier of PDs based on a second type of flash-based PDs,such as MLC. Generally, the SLC PDs may have a higher write enduranceand speed than MLC PDs.

The data storage array may also include different types of adapters ordirectors, such as an HA 21 (host adapter), RA 40 (remote adapter),and/or device interface 23. Each of the adapters may be implementedusing hardware including a processor with local memory with code storedthereon for execution in connection with performing differentoperations. The HAs may be used to manage communications and dataoperations between one or more host systems and the global memory (GM).In an embodiment, the HA may be a Fibre Channel Adapter (FA) or otheradapter which facilitates host communication. The HA 21 may becharacterized as a front end component of the data storage system whichreceives a request from the host. The data storage array may include oneor more RAs that may be used, for example, to facilitate communicationsbetween data storage arrays. The data storage array may also include oneor more device interfaces 23 for facilitating data transfers to/from thedata storage devices 16 a-16 n. The data storage interfaces 23 mayinclude device interface modules, for example, one or more disk adapters(DAs) (e.g., disk controllers), adapters used to interface with theflash drives, and the like. The DAs may also be characterized as backend components of the data storage system which interface with thephysical data storage devices.

One or more internal logical communication paths may exist between thedevice interfaces 23, the RAs 40, the HAs 21, and the memory 26. Anembodiment, for example, may use one or more internal busses and/orcommunication modules. For example, the global memory portion 25 b maybe used to facilitate data transfers and other communications betweenthe device interfaces, HAs and/or RAs in a data storage array. In oneembodiment, the device interfaces 23 may perform data operations using acache that may be included in the global memory 25 b, for example, whencommunicating with other device interfaces and other components of thedata storage array. The other portion 25 a is that portion of memorythat may be used in connection with other designations that may vary inaccordance with each embodiment.

The particular data storage system as described in this embodiment, or aparticular device thereof, such as a disk or particular aspects of aflash device, should not be construed as a limitation. Other types ofcommercially available data storage systems, as well as processors andhardware controlling access to these particular devices, may also beincluded in an embodiment. Furthermore, the data storage devices 16 a-16n may be connected to one or more controllers (not shown). Thecontrollers may include storage devices associated with the controllers.Communications between the controllers may be conducted viainter-controller connections. Thus, the current techniques describedherein may be implemented in conjunction with data storage devices thatcan be directly connected or indirectly connected through anothercontroller.

Host systems provide data and access control information throughchannels to the storage systems, and the storage systems may alsoprovide data to the host systems also through the channels. The hostsystems do not address the drives or devices 16 a-16 n of the storagesystems directly, but rather access to data may be provided to one ormore host systems from what the host systems view as a plurality oflogical devices, logical volumes (LVs) which may also referred to hereinas logical units (e.g., LUNs). A logical unit (LUN) may be characterizedas a disk array or data storage system reference to an amount of diskspace that has been formatted and allocated for use to one or morehosts. A logical unit may have a logical unit number that is an I/Oaddress for the logical unit. As used herein, a LUN or LUNs may refer tothe different logical units of storage which may be referenced by suchlogical unit numbers. The LUNs may or may not correspond to the actualor physical disk drives or more generally physical storage devices. Forexample, one or more LUNs may reside on a single physical disk drive,data of a single LUN may reside on multiple different physical devices,and the like. Data in a single data storage system, such as a singledata storage array, may be accessed by multiple hosts allowing the hoststo share the data residing therein. The HAs may be used in connectionwith communications between a data storage array and a host system. TheRAs may be used in facilitating communications between two data storagearrays. The DAs may be one type of device interface used in connectionwith facilitating data transfers to/from the associated disk drive(s)and LUN (s) residing thereon. A flash device interface may be anothertype of device interface used in connection with facilitating datatransfers to/from the associated flash devices and LUN(s) residingthereon. It should be noted that an embodiment may use the same or adifferent device interface for one or more different types of devicesthan as described herein.

In an embodiment in accordance with techniques herein, the data storagesystem as described may be characterized as having one or more logicalmapping layers in which a logical device of the data storage system isexposed to the host whereby the logical device is mapped by such mappinglayers of the data storage system to one or more physical devices.Additionally, the host may also have one or more additional mappinglayers so that, for example, a host side logical device or volume ismapped to one or more data storage system logical devices as presentedto the host.

A map kept by the storage array may associate logical addresses in thehost visible LUs with the physical device addresses where the dataactually is stored. The map also contains a list of unused slices on thephysical devices that are candidates for use when LUs are created orwhen they expand. The map in some embodiments may also contains otherinformation such as time last access for all or a subset of the slicesor frequency counters for the slice; the time last access or frequencycounters. This information can be analyzed to derive a temperature ofthe slices which can indicate the activity level of data at the slicelevel.

The map, or another similar map, may also be used to store informationrelated to write activity (e.g., erase count) for multiple drives in thestorage array. This information can be used to identify drives havinghigh write related wear relative to other drives having a relatively lowwrite related wear.

The device interface, such as a DA, performs I/O operations on aphysical device or drive 16 a-16 n. In the following description, dataresiding on a LUN may be accessed by the device interface following adata request in connection with I/O operations that other directorsoriginate. The DA which services the particular physical device mayperform processing to either read data from, or write data to, thecorresponding physical device location for an I/O operation.

Also shown in FIG. 1 is a management system 22 a that may be used tomanage and monitor the system 12. In one embodiment, the managementsystem 22 a may be a computer system which includes data storage systemmanagement software such as may execute in a web browser. A data storagesystem manager may, for example, view information about a current datastorage configuration such as LUNs, storage pools, and the like, on auser interface (UI) in display device of the management system 22 a.

It should be noted that each of the different adapters, such as HA 21,DA or disk interface, RA, and the like, may be implemented as a hardwarecomponent including, for example, one or more processors, one or moreforms of memory, and the like. Code may be stored in one or more of thememories of the component for performing processing.

The device interface, such as a DA, performs I/O operations on aphysical device or drive 16 a-16 n. In the following description, dataresiding on a LUN may be accessed by the device interface following adata request in connection with I/O operations that other directorsoriginate. For example, a host may issue an I/O operation which isreceived by the HA 21. The I/O operation may identify a target locationfrom which data is read from, or written to, depending on whether theI/O operation is, respectively, a read or a write operation request. Thetarget location of the received I/O operation may be expressed in termsof a LUN and logical address or offset location (e.g., LBA or logicalblock address) on the LUN. Processing may be performed on the datastorage system to further map the target location of the received I/Ooperation, expressed in terms of a LUN and logical address or offsetlocation on the LUN, to its corresponding physical storage device (PD)and location on the PD. The DA which services the particular PD mayfurther perform processing to either read data from, or write data to,the corresponding physical device location for the I/O operation.

It should be noted that an embodiment of a data storage system mayinclude components having different names from that described herein butwhich perform functions similar to components as described herein.Additionally, components within a single data storage system, and alsobetween data storage systems, may communicate using any suitabletechnique that may differ from that as described herein for exemplarypurposes. For example, element 12 of FIG. 1 may be a data storagesystem, such as the VNXe® Data Storage System by EMC Corporation ofHopkinton, Mass., that includes multiple storage processors (SPs). Eachof the SPs 27 may be a CPU including one or more “cores” or processorsand each may have their own memory used for communication between thedifferent front end and back end components rather than utilize a globalmemory accessible to all storage processors. In such embodiments, memory26 may represent memory of each such storage processor.

An embodiment in accordance with techniques herein may have one or moredefined storage tiers. Each tier may generally include physical storagedevices or drives having one or more attributes associated with adefinition for that tier. For example, one embodiment may provide a tierdefinition based on a set of one or more attributes or properties. Theattributes may include any one or more of a storage type or storagetechnology, device performance characteristic(s), RAID (Redundant Arrayof Independent Disks) group configuration, storage capacity, and thelike. RAID groups are known in the art. The PDs of each RAID group mayhave a particular RAID level (e.g., RAID-1, RAID-5 3+1, RAID-5 7+1, andthe like) providing different levels of data protection. For example,RAID-1 is a group of PDs configured to provide data mirroring where eachdata portion is mirrored or stored on 2 PDs of the RAID-1 group. Thestorage type or technology may specify whether a physical storage deviceis an SSD (solid state drive) drive (such as a flash drive), aparticular type of SSD drive (such using flash memory or a form of RAM),a type of rotating magnetic disk or other non-SSD drive (such as a 10KRPM rotating disk drive, a 15K RPM rotating disk drive), and the like.

Performance characteristics may relate to different performance aspectsof the physical storage devices of a particular type or technology. Forexample, there may be multiple types of rotating disk drives based onthe RPM characteristics of the disk drives where disk drives havingdifferent RPM characteristics may be included in different storagetiers. Storage capacity may specify the amount of data, such as inbytes, that may be stored on the drives. An embodiment may define one ormore such storage tiers. For example, an embodiment in accordance withtechniques herein that is a multi-tiered storage system may define twostorage tiers including a first tier of all SSD drives and a second tierof all non-SSD drives. As another example, an embodiment in accordancewith techniques herein that is a multi-tiered storage system may definethree storage tiers including a first tier of all SSD drives which areflash drives, a second tier of all 15K RPM rotating disk drives, and athird tier of all 10K RPM rotating disk drives. In terms of generalexpected performance, the SSD or flash tier may be considered thehighest performing tier. The second tier of 15K RPM disk drives may beconsidered the second or next highest performing tier and the 10K RPMdisk drives may be considered the lowest or third ranked tier in termsof expected performance. The foregoing are some examples of tierdefinitions and other tier definitions may be specified and used in anembodiment in accordance with techniques herein.

In a data storage system in an embodiment in accordance with techniquesherein, PDs may be configured into a pool or group of physical storagedevices where the data storage system may include many such pools of PDssuch as illustrated in FIG. 2. Each pool may include one or moreconfigured RAID groups of PDs.

Depending on the particular embodiment, each pool may also include onlyPDs of the same storage tier with the same type or technology, or mayalternatively include PDs of different storage tiers with differenttypes or technologies.

The techniques herein may be generally used in connection with any typeof flash device, or more generally, any SSD technology. The flash devicemay be, for example, a flash device which is a NAND gate flash device,NOR gate flash device, flash device that uses SLC or MLC technology, andthe like. In one embodiment, the one or more flash devices may includeMLC flash memory devices although an embodiment may utilize MLC, aloneor in combination with, other types of flash memory devices or othersuitable memory and data storage technologies. More generally, thetechniques herein may be used in connection with other SSD technologiesalthough particular flash memory technologies may be described hereinfor purposes of illustration. For example, consistent with descriptionelsewhere herein, an embodiment may define multiple storage tiersincluding one tier of PDs based on a first type of flash-based PDs, suchas based on SLC technology, and also including another different tier ofPDs based on a second type of flash-based PDs, such as MLC. Generally,the SLC PDs may have a higher write endurance and speed than MLC PDs.

With reference to FIG. 2, a first pool, pool 1 206 a, may include twoRAID groups (RGs) of 10K RPM rotating disk drives of a first storagetier. The foregoing two RGs are denoted as RG1 202 a and RG2 202 b. Asecond pool, pool 2 206 b, may include 1 RG (denoted RG3 204 a) of 15KRPM disk drives of a second storage tier of PDs having a higher relativeperformance ranking than the first storage tier of 10K RPM drives. Athird pool, pool 3 206 c, may include 2 RGs (denoted RG 4 204 b and RG 5204 c) each of which includes only flash-based drives of a third highestperformance storage tier of PDs having a higher relative performanceranking than both the above-noted first storage tier of 10K RPM drivesand second storage tier of 15K RPM drives.

The components illustrated in the example 200 below the line 210 may becharacterized as providing a physical view of storage in the datastorage system and the components illustrated in the example 200 abovethe line 210 may be characterized as providing a logical view of storagein the data storage system. The pools 206 a-c of the physical view ofstorage may be further configured into one or more logical entities,such as LUNs or more generally, logical devices. For example, LUNs 212a-m may be thick or regular logical devices/LUNs configured or havingstorage provisioned, from pool 1 206 a. LUN 220 a may be a virtuallyprovisioned logical device, also referred to as a virtually provisionedLUN, thin device or thin LUN, having physical storage configured frompools 206 b and 206 c. A thin or virtually provisioned device isdescribed in more detail in following paragraphs and is another type oflogical device that may be supported in an embodiment of a data storagesystem in accordance with techniques herein.

Generally, a data storage system may support one or more different typesof logical devices presented as LUNs to clients, such as hosts. Forexample, a data storage system may provide for configuration of thick orregular LUNs and also virtually provisioned or thin LUNs, as mentionedabove. A thick or regular LUN is a logical device that, when configuredto have a total usable capacity such as presented to a user for storingdata, has all the physical storage provisioned for the total usablecapacity. In contrast, a thin or virtually provisioned LUN having atotal usable capacity (e.g., a total logical capacity as published orpresented to a user) is one where physical storage may be provisioned ondemand, for example, as data is written to different portions of theLUN's logical address space. Thus, at any point in time, a thin orvirtually provisioned LUN having a total usable capacity may not have anamount of physical storage provisioned for the total usable capacity.

The granularity or the amount of storage provisioned at a time forvirtually provisioned LUN may vary with embodiment. In one embodiment,physical storage may be allocated, such as a single allocation unit ofstorage, the first time there is a write to a particular target logicaladdress (e.g., LUN and location or offset on the LUN). The singleallocation unit of physical storage may be larger than the size of theamount of data written and the single allocation unit of physicalstorage is then mapped to a corresponding portion of the logical addressrange of a LUN. The corresponding portion of the logical address rangeincludes the target logical address. Thus, at any point in time, not allportions of the logical address space of a virtually provisioned devicemay be associated or mapped to allocated physical storage depending onwhich logical addresses of the virtually provisioned LUN have beenwritten to at a point in time.

In one embodiment, a thin device may be implemented as a first logicaldevice, such as 220 a, mapped to portions of one or more second logicaldevices, also referred to as data devices. Each of the data devices maybe subsequently mapped to physical storage of underlying storage pools.For example, portions of thin device 220 a may be mapped tocorresponding portions in one or more data devices of the first group222 and/or one or more data devices 216 a-n of the second group 224.Data devices 214 a-n may have physical storage provisioned in a mannerlike thick or regular LUNs from pool 206 b. Data devices 216 a-n mayhave physical storage provisioned in a manner like thick or regular LUNs(e.g., similar to LUNs A1-Am 212 a-212 m) from pool 206 c. Thus,portions of thin device 220 a mapped to data devices of 222 have theirdata stored on 15K RPM PDs of pool 206 b, and other portions of thindevice 220 a mapped to data devices of 224 have their data stored onflash PDs of pool 206 c. In this manner, storage for different portionsof thin device 220 a may be provisioned from multiple storage tiers.

In at least one embodiment as described herein, the particular storagetier upon which a data portion of a thin device is stored may vary withthe I/O workload directed to that particular data portion. For example,a first data portion of thin device 220 a having a high I/O workload maybe stored on a PD of pool 206 c by mapping the first logical address ofthe first data portion in the thin LUN's address space to a secondlogical address on a data device in 224. In turn the second logicaladdress of the data device in 224 may be mapped to physical storage ofpool 206 c. A second data portion of thin device 220 a having a lowerI/O workload than the first data portion may be stored on a PD of pool206 b by mapping the third logical address of the second data portion inthe thin LUN's address space to a fourth logical address on a datadevice in 222. In turn the fourth logical address of the data device in222 may be mapped to physical storage of pool 206 b. As the I/O workloadof the foregoing two data portions of thin device 220 a may vary, thedata portions may be relocated to a different storage tier. For example,if the workload of the second data portion greatly increases at a laterpoint in time, the second data portion may be relocated or moved to pool206 c by mapping its corresponding third logical address in the thindevice 220 a's address space to a fifth logical address of a data devicein 224 where the fifth logical address is mapped to physical storage onpool 206 c. The foregoing is described in more detail elsewhere herein.

In some embodiments, the data devices of 222 and 224 may not be directlyuseable (visible) to hosts coupled to a data storage system. Each of thedata devices may correspond to one or more portions (including a wholeportion) of one or more of the underlying physical devices. As notedabove, the data devices 222 and 224 may be designated as correspondingto different performance classes or storage tiers, so that differentones of the data devices of 222 and 224 correspond to different physicalstorage having different relative access speeds and/or different RAIDprotection type (or some other relevant distinguishing characteristic orcombination of characteristics), as further discussed elsewhere herein.

As shown in FIG. 3, the data storage system 124 may also include aplurality of thin devices 71-74 that may be adapted for use inconnection with the system described herein when using thinprovisioning. Consistent with discussion elsewhere herein, in a systemusing thin provisioning, the thin devices 71-74 may appear to a hostcoupled to the storage system 124 as one or more logical volumes(logical devices) containing contiguous blocks of data storage. Each ofthe thin devices 71-74 may contain pointers to some or all of the datadevices 61-67 (or portions thereof). As described in more detailelsewhere herein, a thin device may be virtually provisioned in terms ofits allocated physical storage in physical storage for a thin devicepresented to a host as having a particular capacity is allocated asneeded rather than allocate physical storage for the entire thin devicecapacity upon creation of the thin device. As such, a thin devicepresented to the host as having a capacity with a corresponding LBA(logical block address) range may have portions of the LBA range forwhich storage is not allocated.

Referring to FIG. 4, shown is an example 700 illustrating use of a thindevice in an embodiment in accordance with techniques herein. Theexample 700 includes three storage pools 712, 714 and 716 with each suchpool representing a storage pool of a different storage tier. Forexample, pool 712 may represent a storage pool of tier A of flashstorage devices, pool 714 may represent a storage pool of tier B of 15KRPM storage devices, and pool 716 may represent a storage pool of tier Cof 10K RPM storage devices. Each storage pool may include a plurality oflogical devices which are data devices mapped to the pool's underlyingphysical devices (or portions thereof). Element 702 represents the thindevice address space or range including chunks which are mapped todifferent storage pools. For example, element 702 a denotes a chunk C1which is mapped to storage pool 712 and element 702 b denotes a chunk C2which is mapped to storage pool 714. Element 702 may be a representationfor a first thin device which is included in a storage group of one ormore thin devices.

It should be noted that although the example 700 illustrates only asingle storage pool per storage tier, an embodiment may also havemultiple storage pools per tier.

Referring to FIG. 5, shown is an example representation of informationthat may be included in an allocation map in an embodiment in accordancewith techniques herein. An allocation map may be used to identify themapping for each thin device (TD) chunk (e.g. where each chunk isphysically located). Element 760 represents an allocation map that maybe maintained for each TD. In this example, element 760 representsinformation as may be maintained for a single TD although anotherallocation map may be similarly used and maintained for each other TD ina storage group. Element 760 may represent mapping information asillustrated in FIG. 4 such as in connection the mapping of 702 todifferent storage pool devices. The allocation map 760 may contain anentry for each chunk and identify which data device and associatedphysical storage is mapped to the chunk. For each entry or row of themap 760 corresponding to a chunk, a first column 760 a, Chunk ID,denotes an identifier to uniquely identify the chunk of the TD, a secondcolumn 760 b, indicates information about the data device and offset towhich the chunk is mapped, and a third column storage pool 760 c denotesthe storage pool and tier including the data device of 760 b. Forexample, entry 762 represents chunk C1 illustrated in FIG. 4 as 702 aand entry 764 represents chunk C2 illustrated in FIG. 4 as 702 b. Itshould be noted that although not illustrated, the allocation map mayinclude or otherwise use other tables and structures which identify afurther mapping for each data device such as which physical devicelocations map to which data devices. This further mapping for each datadevice is described and illustrated elsewhere herein. Such informationas illustrated and described in connection with FIG. 5 may be maintainedfor each thin device in an embodiment in accordance with techniquesherein.

Thin devices and thin provisioning, also referred to respectively asvirtually provisioned devices and virtual provisioning, are described inmore detail, for example, in U.S. patent application Ser. No.11/726,831, filed Mar. 23, 2007 (U.S. Patent App. Pub. No. 2009/0070541A1), entitled AUTOMATED INFORMATION LIFE-CYCLE MANAGEMENT WITH THINPROVISIONING, and U.S. Pat. No. 7,949,637, Issued May 24, 2011, entitledSTORAGE MANAGEMENT FOR FINE GRAINED TIERED STORAGE WITH THINPROVISIONING, both of which are incorporated by reference herein.

Referring to FIG. 6, shown is an example 100 of components that may beused in an embodiment in connection with techniques herein. The example100 includes performance data monitoring software 134 which gathersperformance data about the data storage system. The software 134 maygather and store performance data 136. This performance data 136 mayalso serve as an input to other software, such as used by the datastorage optimizer 135 in connection with performing data storage systemoptimizations, which attempt to enhance the performance of I/Ooperations, such as those I/O operations associated with data storagedevices 16 a-16 n of the system 12 (as in FIG. 1). For example, theperformance data 136 may be used by a data storage optimizer 135 in anembodiment in accordance with techniques herein. The performance data136 may be used in determining and/or optimizing one or more statisticsor metrics such as may be related to, for example, a wear rate for oneor more physical devices, a pool or group of physical devices, logicaldevices or volumes (e.g., LUNs), thin or virtually provisioned devices(described in more detail elsewhere herein), portions of thin devices,and the like. The wear rate may also be a measurement or level of “howbusy” a device is, for example, in terms of write operations or PEcycles.

In one embodiment in accordance with techniques herein, components ofFIG. 6, such as the performance monitoring software 134, performancedata 136 and/or data storage optimizer 135, may be located and executeon a system or processor that is external to the data storage system. Asan alternative or in addition to having one or more components executeon a processor, system or component external to the data storage system,one or more of the foregoing components may be located and execute on aprocessor of the data storage system itself.

It should be noted that the back-end (e.g., physical device) writeoperations with respect to a LUN, thin device, and the like, may beviewed as write requests or commands from the DA 23, controller or otherbackend physical device interface. Thus, these are operations may alsobe characterized as a number of operations with respect to the physicalstorage device (e.g., number of physical device writes based on physicaldevice accesses). This is in contrast to observing or counting a numberof particular type of I/O requests (e.g., reads or writes) as issuedfrom the host and received by a front end component such as an HA 21.For example, when writing data of a received host I/O request to thephysical device, the host write request may result in multiple readsand/or writes by the DA 23 in addition to writing out the host or userdata of the request. If the data storage system implements a RAID dataprotection technique, such as RAID-5, additional reads and writes may beperformed such as in connection with writing out additional parityinformation for the user data. Thus, observed data gathered to determinewear rate, such as observed numbers writes may refer to the writerequests or commands performed by the DA. Such write commands maycorrespond, respectively, to physical device accesses such as diskwrites that may result from a host I/O request received by an HA 21.

The optimizer 135 may perform processing to determine how to allocate orpartition physical storage in a multi-tiered environment for use bymultiple applications. The optimizer 135 may perform processing such as,for example, to determine what particular portions of LUNs, such as thindevices, to store on physical devices of a particular tier, evaluatewhen to move data between physical drives of different pools, tiers, andthe like. Such data portions of a thin device may be automaticallyplaced in a storage pool. The data portions may also be automaticallyrelocated or moved to a different storage pool as the SSD wear rate andobserved performance characteristics for the data portions change overtime. In accordance with techniques herein, analysis of wear rate fordata portions of thin devices may be performed in order to determinewhether particular data portions should have their data contents storedon physical devices located in a particular storage pool. It should benoted that the optimizer 135 may generally represent one or morecomponents that perform processing as described herein as well as one ormore other optimizations and other processing that may be performed inan embodiment.

Promotion may refer to movement of data from a source storage tier to atarget storage tier where the target storage tier is characterized ashaving devices of higher performance than devices of the source storagetier. For example movement of data from a tier of 10K RPM drives to atier of SSDs may be characterized as a promotion and may be performedwhen the SSD wear rate directed to the relocated data increases.Demotion may refer generally to movement of data from a source storagetier to a target storage tier where the source storage tier ischaracterized as having devices of higher performance than devices ofthe target storage tier. For example movement of data from a tier ofSSDs to a tier of 10K RPM drives may be characterized as a demotion andmay be performed when the SSD wear rate directed to the relocated datadecreases.

An embodiment may use a data storage optimizer such as, for example,EMC® Fully Automated Storage and Tiering for Virtual Pools (FAST VP) byEMC Corporation, providing functionality as described herein for suchautomated evaluation and data movement optimizations. For example,different techniques that may be used in connection with the datastorage optimizer are described in U.S. patent application Ser. No.13/466,775, filed May 8, 2012, PERFORMING DATA STORAGE OPTIMIZATIONSACROSS MULTIPLE DATA STORAGE SYSTEMS, which is incorporated by referenceherein.

In at least one embodiment in accordance with techniques herein, one ormore I/O statistics may be observed and collected for individualpartitions, or slices of each LUN, such as each thin or virtuallyprovisioned LUN. The logical address space of each LUN may be dividedinto partitions each of which corresponds to a subrange of the LUN'slogical address space. Thus, I/O statistics may be maintained forindividual partitions or slices of each LUN where each such partition orslice is of a particular size and maps to a corresponding subrange ofthe LUN's logical address space.

An embodiment may have different size granularities or units. Forexample, consider a case for a thin LUN having a first logical addressspace where I/O statistics may be maintained for a first slice having acorresponding logical address subrange of the first logical addressspace.

The embodiment may allocate physical storage for thin LUNs in allocationunits referred to as chunks. In some cases, there may be multiple chunksin a single slice (e.g. where each chunk may be less than the size of aslice for which I/O statistics are maintained). Thus, the entirecorresponding logical address subrange of the first slice may not bemapped to allocated physical storage depending on what logical addressesof the thin LUN have been written to. Additionally, the embodiment mayperform data movement or relocation optimizations based on a datamovement size granularity. In at least one embodiment, the data movementsize granularity or unit may be the same as the size of a slice forwhich I/O statistics are maintained and collected.

In at least one embodiment of a data storage system using techniquesdescribed herein, a fixed size slice may be used for each LUN's logicaladdress space. For example, the size of each slice may be 256 megabytes(MB) thereby denoting that I/O statistics are collected for each 256 MBportion of logical address space and where data movement optimizationsare performed which relocate or move data portions which are 256 MB insize. In such an embodiment, data may be allocated for thin devices inchunks where, generally, the size of a slice is some integer multiple ofa chunk (e.g., there may be one or multiple chunks in a single slice).In at least one embodiment, storage may be allocated for thin devices inchunks which are each 256 MB or the same size as a slice whereby thesize granularity for data movement, thin device allocation andstatistics collection may be the same.

In one embodiment, I/O statistics or metrics maintained for slices, ormore generally, data portions, of a LUN may reflect I/O activity or SSDwear rate expressed, for example, write operation per hour and wearratio (as will be further explained below). It should be noted that moregenerally, any suitable I/O statistic may be used to measure the SSDwear rate of data portions to select which data portions belong on whichSSD.

In one embodiment in accordance with techniques herein, the data storageoptimizer may collect information regarding SSD wear rate of dataportions for one or more time periods and use such information inconnection with predicting and modeling SSD wear rate of the dataportions for the next time period. Based on predicted SSD wear rates forthe data portions, for example, for a next time period N+1, the datastorage optimizer may select data portions for placement or movement todifferent SSDs. The data storage system may model the movement orplacement of the data portions for the next time period N+1 using thepredicted SSD wear rates for the data portions in order to determine,for example, overall data storage system performance, per storage tierperformance, and the like. Based on such modeled or simulatedperformance of the data storage system, storage pools or tiers, and thelike, if a selected set of data portion movements were performed, adecision may be made as to whether to actually implement or perform themodeled data movements or otherwise consider an alternative set of datamovements.

FIG. 7 depicts a graphical representation illustrating SSD wear datacollection and analysis techniques according to an example embodiment.With reference to logical address space corresponding to a particularslice, slice statistics may be generated for each slice that include,but not limited to, number of IOPs, number of blocks written. Flashdrive statistics may also be generated for each SSD that includes thedrive's maximum PE cycle count, current PE cycle count, and hours to endof warranty (EOW).

The left Y axis 705 represents the number of bytes or blocks written toa SSD. This may be determined by summing the slice statistics for all orsubstantially all the slices stored on a particular SSD. Thus, the sumof the bytes written to each slice may represent the number of byteswritten to the corresponding SSD. The right Y axis 710 represents thenumber of current PE cycles for the SSD. The current PE cycle, max PEcycle, and hours to EOW may be determined by querying the SSD ofinterest and/or a corresponding data structure maintained by storagesystem. The X axis represents time over which the bytes are written andPE cycles occur. When the graph is viewed as a whole, the activity line715 represents the Y 705 number of bytes written to the SSD that causesthe current PE cycle to increase by X, that is, how many bytes causesthe PE cycle count to increase. Put another way, as Y 705 number ofbytes causes X 710 change in cycle count, then Y/X bytes written causesthe PE cycle to increase by 1.

Given that an SSD has a max PE cycle count and that we can determine thecurrent PE count, the remaining number of PE cycles to EOW can becalculated by subtracting the current PE cycle count from the max PEcycle count. With this information and calculating Y/X as describedabove, the number of bytes that can be written to the SSD before the SSDreaches EOW can be calculated as follows:

Bytes written to EOW=(Max PE−Current PE)*(Y/X)  EQUATION 1

SSDs can be rated as having a number of writes per hour to EOW. Forexample, a SSD may be specified as being able to perform 3 writes perhour for a period of 5 years. If we know that a drive has W hours toEOW, the number of bytes per hour that can be written to the SSD beforeit reaches EOW may be calculated as follows:

Q=(Max PE−Current PE)*(Y/X)*W;  EQUATION 2

Where Q=bytes written per hour to reach EOW, and W is number of hoursuntil EOW

Thus, if Q bytes are written per hour, the drive will not wear outbefore the EOW period.

FIG. 8 is a graphical representation illustrating an example embodimentemploying the techniques described herein. The left Y axis 805represents the number of bytes written to a particular slice. The rightY axis 810 represents a predicted number of bytes that will be writtenin the next time interval, the time axis is segmented according to thetime intervals.

Data storage systems employing data movement methods such as the FASTmethods described elsewhere herein, slice data typically exhibitsspecial and temporal locality access characteristics that enablepredicting the number of bytes that will be written to a particularslice in a next time interval based on previous write activity. Asdescribed above, slice statistics are determined for each slice storedon the data storage system and these statistics can be used to estimatethe number of bytes that will be written to the slice during the nexttime interval. For example, in one example embodiment, the predictednumber of bytes written to a slice in the next time interval may beestimated performing an linear or similar extrapolation of bytes writtenduring a number of previous time intervals. In another exampleembodiment, a linear or similar extrapolation may be performed. Inanother embodiment, a moving average using n samples as a history may beused. In another example embodiment, simply the number of bytes writtenin the previous time interval may be used, where the smaller the timeinterval, the closer the estimate will track the actual number of byteswritten. Other estimation methods may be similarly implemented.

Using the techniques described above for analyzing slice and driveinformation, the estimated number of bytes to be written to a SSD can bedetermined. For example, for a particular SSD, the slices stored on theSSD can be determined. The number of the estimated writes for all theslices stored on the SSD can be calculated to determine the of estimatedwrites for the SSD. With this information, a ratio representing SSD wearrate may be determined using the following:

Wear rate=SumWR/Q  EQUATION 3

where SumWR is the estimated number of writes for a SSD and Q isdetermined using EQUATION 2 as described above. Accordingly, increasingSumWR increases the ratio value, representing an increased wear rate;conversely decreasing SumWR decrease the ratio value, representing adecrease wear rate. Thus, determining slice statistics and analyzingdrive parameters provides the ability to determine a SSD's wear rate.Executing the technique for a set of SSDs enables identifying SSDs thatmay wear out before a specified warranty period. The technique furtherprovided a mechanism to identify slices on such drives and move one ormore slices to drives having lower wear rates so as to balance wearacross a set of drives or substantially all the drives in a storagesystem.

FIG. 9 illustrates an example embodiment 900 of a data storage systemimplementing the techniques described herein. Shown are a plurality offlash drives arranged into three SSD RAID group configurations where SSDRAID group 905 includes flash drives D0-D3, SSD RAID group 910 includesflash drives D10-D13, and SSD RAID group 915 includes flash drivesD20-D23. Initially, RAID group 905 has slices 1-2 stored thereon, andRAID group 915 has slices 21-22 stored on it and RAID group 910 is empty(e.g., just installed). Although the technique is shown as applied toRAID groups, the technique can be applied to as few as one flash driveto essentially an entire storage array.

RAID group 905 has a max PE cycle specification of 500, where thecurrent PE cycle count=400 and, therefore, the remaining PE cyclecount=100. X=100, which represents, the number of bytes that causes Y,the PE count, to increase by 1. Thus, Y/X=1/100=0.01. W, the number oftime intervals at which the EOW is reached=100. Consequently, applyingEQUATION 2 as discussed above, Q=(Remaining PEcount)*(Y/X)*W=(100)*(0.01)*100=100. After analyzing drive statistics,the technique turns to the slices stored on the RAID group 905 flashdrives. WR represents the estimated number of bytes that will be writtento a particular slice. Here, slice 1 has a WR=100 and slice 2 has aWR=150. Applying EQUATION 3, the wear rate ratio for RAID group905=SumWR/Q=(100+150)/100=2.5. At this rate, the flash drives will wearout before the EOW is reached.

The technique is applied to the next RAID group in a similar manner. Forexample, RAID group 915 has a max PE cycle specification of 800, wherethe current PE cycle count=600 and, therefore, the remaining PE cyclecount=200. X=100, which represents, the number of bytes that causes Y,the PE count, to increase by 1. Thus, Y/X=1/100=0.01. W, the number oftime intervals at which the EOW is reached=100. Consequently, applyingEQUATION 2 as discussed above, Q=(Remaining PEcount)*(Y/X)*W=(200)*(0.01)*100=200. After analyzing drive statistics,the technique turns to the slices stored on the RAID group 915 flashdrives. WR represents the estimated number of bytes that will be writtento a particular slice. Here, slice 21 has a WR=150 and slice 2 has aWR=250. Applying EQUATION 3, the wear rate ratio for RAID group915=SumWR/Q=(300+250)/200=2.75. At this rate, the flash drives of RAIDgroup 915 will also wear out before the EOW is reached.

RAID group 910 is a group of flash drives that have a very low wear rate(e.g., a newly installed or newly provisioned RAID group). The techniquemay the implemented in a similar manner to determine that the wear rateratio is close to zero. To balance wear across all the flash drivesevenly, the technique moves one or more slices to adjust the wear rateso that drives experiencing a high wear rate is reduced and moved todrives experience a low wear rate. In this example, slice 1 is movedfrom RAID group 905 to RAID group 910 and slice 22 is moved from RAIDgroup 915 to RAID group 910.

FIG. 10 depicts a flow diagram illustrating example embodiments of amethod 1000 according to various implementations for use in balancingSSD wear in data storage systems. While various methods disclosed hereinare shown in relation to a flowchart or flowcharts, it should be notedthat any ordering of method steps implied by such flowcharts or thedescription thereof is not to be construed as limiting the method toperforming the steps, or sub-steps within or among the steps, in thatorder. Rather, the various steps of each of the methods disclosed hereincan be performed in any of a variety of sequences. In addition, as theillustrated flowcharts are merely example embodiments, various othermethods that include additional steps or include fewer steps thanillustrated are also within the scope of the present invention. Theoperations may be performed in hardware, or as processor-executableinstructions that may be executed by a processor. Furthermore, themethod 1000 may, but need not necessarily, be implemented using the datastorage system of FIG. 1 and may also be implemented, in or incombination with, for example, a server, storage appliance, networkdevice, cloud storage system, virtualization appliance, software definedstorage, or other such implementation comprising or exercising flashbased SSDs. The SSDs may be constructed using different types of memorytechnologies such as nonvolatile semiconductor NAND flash memory formingone or more SLC devices and/or MLC devices. The SSDs may be arranged ina RAID configuration in one or more data storage systems. Alternatively,or in addition, flash drives may be configured as a storage tier in thedata storage system, wherein the storage tier is one of multiple storagetiers, the multiple storage tiers having progressively better responsetime characteristics.

Referring to FIG. 10, with reference to the system of FIG. 1 and theSSDs of FIG. 9, the method 1000 provides a mechanism to, for example,identify the wear rate of an SSD or flash drive. When data is arranged,for example, as a slice stored on a LUN, the slices are mapped tophysical drives using a mapping layer. The data may be stored such thata first RAID group(s) stores slices that are write heavy while a secondRAID group(s) stores less write heavy and/or read heavy data slices. Insuch a case, the first RAID group will experience a wear ratesignificantly higher than the second RAID group. Since SSD flash driveshave a limited write capability, the first RAID group may fail earlierthan desired. For example, a storage array comprising SSD flash drivesmay have a 5 year warranty period. The array may be designed such thatan SSD flash drive engineered perform a certain number of writeoperations over the 5 year warranty, and under normal operations, suchwarranty periods are sufficiently satisfied. However, extreme wearpatterns such as those described above may cause an SSD to wear fasterthat the systems design parameters resulting in a failure that issubject to a warranty claim. Conversely, a drive may experiencesignificantly less write wear, and as a result, continue to operate wellbeyond it's warranty period. In this case, presuming that a user wantsto make full use of performance an SSD offers, such and extension beyondexpected operating life may be considered unused performance.Furthermore, the low wear rate SSD may be used to absorb wear beingdirected to the high wear rate SSD, thereby reducing its wear rate andextending its useful life.

The example embodiment depicted in FIG. 10 provides a mechanism topredict the wear rate of multiple SSD and balance the wear rate of themultiple SSDs such that they wear at approximately the same rate. Itshould be noted that although the techniques discuss SSDs in relation toa data storage system in various example embodiments, the techniques maybe used in other systems having SSDs where the write commands may besent to, for example, a server or virtualized storage where the flashwear reduction and performance improvements techniques may be similarlyapplied.

At step 1005, the method identifies multiple sets of flash drives, whereeach set of flash drives are arranged to store multiple slices of datawhere the slices are striped across a group of SSD in, for example, aRAID configuration. Although the technique is described using RAIDconfiguration, various alternative embodiments may implement othervarious configurations and arrangements.

At step 1010, the method predicts a write rate for each set of flashdrives. That is, for each slice stored on the set of flash drives, therate as which data will be written to the flash drive in the next timeinterval will be predicted. In one embodiment, the pervious actual datawrite rate will be used. In the case where the time intervals arerelatively short, as a result of temporal and special locality, thepredicted write rates will be fairly accurate as they will predictablylag the actual rate in an acceptable manner. In other various exampleembodiments, the rate may be determined by performing a moving averageaveraging n previous recorded write rates, performing a linear fit orsimilar such extrapolation. The predicted number of expected writes maybe referred to as WR. Slice and drive information may be analyzed suchthat WR can be determined for each slice on an SSD RAID group. The sumof the expected writes for all the slices stored on RAID group's SSDflash drives may be referred to as SumWR.

At step 1015, the number of remaining PE cycles (i.e., number ofremaining write operations) that can be performed by SSD RAID groupflash drives may be determined. For example, if a RAID group has a maxPE cycle count of 500, and its current PC cycle count is 400, there are100 remaining PE cycles before the drive is at the end of it's specifiedPE cycle count and considered “worn out.” While the drive may not failimmediately, the drive cannot be expected to reliably store data fromthat point forward.

At step 1020, a metric representative of a wear rate may be determinedfor each RAID group in a manner as was discussed in FIG. 9. In oneexample embodiment, the wear metric may be expressed as a ratio SumWR(the sum of the expected writes to slices on the RAID group) and Q (thenumber of write bytes/hour before remaining cycle count=0). Othermetrics using the parameters discussed above may be implemented in asimilar manner. As shown in FIG. 9, RAID group 905 has a determined wearrate of 2.5 and RAID group 915 has a wear rate of 2.75. If these wearrates are determined to be relatively high compared to one or more otherRAID groups, slices stored on RAID groups 905 and 910 may be remapped ormigrated to other RAID groups having a lower wear rate such as RAIDgroup 910.

At step 1025, the method implements a balancing scheme in order tobalance the wear rates across multiple RAID groups such that the RAIDgroup flash SSDs wear at an even rate. Example remapping schemes includecreating a rank ordered table and selecting slices on high wear rateRAID groups and moving them to lower wear rate RAID groups. Otherexample embodiments may implement general multidimensional knapsackapproach, greedy algorithm, and the like.

While the above description refers to a data storage system or arrayhaving flash based SSD, the techniques may be similarly appliedaccording to alternative embodiments directed to other systemsimplementing flash based SSDs such as servers, network processors,compute blocks, converged systems, virtualized systems, and the like.Additionally, it should be appreciated that the technique can apply toblock, file, object and/or content architectures.

It will be appreciated that an embodiment may implement the techniqueherein using code executed by a computer processor. For example, anembodiment may implement the technique herein using code which isexecuted by a processor of the data storage system. As will beappreciated by those skilled in the art, the code may be stored on thedata storage system on any one of a computer-readable medium having anyone of a variety of different forms including volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information such as computer readableinstructions, data structures, program modules or other data. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, (DVD) or other opticalstorage, magnetic cassettes, magnetic tape, magnetic disk storage orother magnetic storage devices, or any other medium which can be used tostore the desired information and which can accessed by a data storagesystem processor.

While various embodiments of the present disclosure have beenparticularly shown and described, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims.

What is claimed is:
 1. A method for use in balancing flash drive wear indata storage systems, the method comprising: identifying multiple setsof flash drives, wherein each set of flash drives store data arranged inmultiple slices striped across the set of flash drives; predicting, foreach set of flash drives, a write rate at which data will be written tothe multiple slices stored on the set of flash drives during a next timeinterval; determining, for each set of flash drives, a number of bytesthat can be written to each set of flash drives, wherein the number isbased on a remaining program/erase (PE) cycle count for each respectiveset of flash drives; determining, for each set of flash drives, a metricrepresentative of a wear rate, the metric based on a respective flashdrives determined predicted write rate and the determined number ofbytes that can be written to each set of flash drives; and balancing thewear rate of the multiple sets of flash drives based on each respectiveflash drives wear rate.
 2. The method as claimed in claim 1, whereinpredicting the write rate includes identifying one or more actual writerates occurring during one or more corresponding time intervalsoccurring substantially immediately prior to the next time interval. 3.The method as claimed in claim 1, wherein predicting the write rateincludes identifying one or more actual write rates occurring during oneor more corresponding time intervals occurring substantially immediatelyprior to the next time interval, wherein the predicted write rate is afunction of the identified one or more actual write rates.
 4. The methodas claimed in claim 1, wherein balancing includes identifying a firstset of flash drives having a higher wear rate than a second set of flashdrives and remapping one or more slices from the first set of flashdrives to the second set of flash drives.
 5. A system for use inbalancing flash drive wear in data storage systems, the systemcomprising: a storage processor and memory configured to: identifymultiple sets of flash drives, wherein each set of flash drives storedata arranged in multiple slices striped across the set of flash drives;predict, for each set of flash drives, a write rate at which data willbe written to the multiple slices stored on the set of flash drivesduring a next time interval; determine, for each set of flash drives, anumber of bytes that can be written to each set of flash drives, whereinthe number is based on a remaining program/erase (PE) cycle count foreach respective set of flash drives; determine, for each set of flashdrives, a metric representative of a wear rate, the metric based on arespective flash drives determined predicted write rate and thedetermined number of bytes that can be written to each set of flashdrives; and balance the wear rate of the multiple sets of flash drivesbased on each respective flash drives wear rate.
 6. A computer-programproduct including a non-transitory computer-readable storage mediumencoded with computer-program code that, when executed on a processor ofa computer, causes the computer to manage data storage in a data storagesystem, the computer-program product further comprising: identifyingmultiple sets of flash drives, wherein each set of flash drives storedata arranged in multiple slices striped across the set of flash drives;predicting, for each set of flash drives, a write rate at which datawill be written to the multiple slices stored on the set of flash drivesduring a next time interval; determining, for each set of flash drives,a number of bytes that can be written to each set of flash drives,wherein the number is based on a remaining program/erase (PE) cyclecount for each respective set of flash drives; determining, for each setof flash drives, a metric representative of a wear rate, the metricbased on a respective flash drives determined predicted write rate andthe determined number of bytes that can be written to each set of flashdrives; and balancing the wear rate of the multiple sets of flash drivesbased on each respective flash drives wear rate.